1. Field of the Invention
The present invention relates to multilayer electronic components and methods for manufacturing the same. More particularly, the present invention relates to a multilayer electronic component in which external electrodes are formed by plating directly on the outer surface of a laminate and a method for manufacturing the same.
2. Description of the Related Art
Referring to FIG. 4, a multilayer electronic component 101, exemplified by a monolithic ceramic capacitor, typically includes a laminate 105 which includes a plurality of stacked insulator layers 102 and a plurality of internal electrodes 103 and 104, extending along the interfaces between the insulator layers 102. An end of each of the plurality of internal electrodes 103 and an end of each of the plurality of internal electrodes 104 are respectively exposed at an end surface 106 and an end surface 107 of the laminate 105. An external electrode 108 is disposed so as to electrically connect the ends of the internal electrodes 103, and an external electrode 109 is disposed so as to electrically connect the ends of the internal electrodes 104.
In order to form the external electrodes 108 and 109, first, a metal paste including a metal component and a glass component is applied on the end surfaces 106 and 107 of the laminate 105, followed by baking to form an electrode paste film 110 on each of the end surfaces 106 and 107. Next, a first plating film 111 including Ni as a major component, for example, is formed on the electrode paste film 110, and a second plating film 112 including Sn as a major component, for example, is further formed thereon. That is, each of the external electrodes 108 and 109 has a three-layered structure including the electrode paste film 110, the first plating film 111, and the second plating film 112.
The external electrodes 108 and 109 are required to have good wettability with respect to solder when the multilayer electronic component 101 is mounted on a substrate by soldering. Furthermore, the external electrode 108 is required to have a function of electrically connecting the plurality of internal electrodes 103 which are electrically isolated from each other, and the external electrode 109 is required to have a function of electrically connecting the plurality of internal electrodes 104 which are electrically isolated from each other. The function of ensuring wettability is provided by the second plating film 112, and the function of electrically connecting the internal electrodes 103 or 104 is provided by the electrode paste film 110. The first plating film 111 has a function of preventing solder leaching during the soldering operation.
However, the thickness of the electrode paste film 110 is relatively large ranging from about several tens of micrometers to several hundred micrometers. Consequently, in order to set the size of the multilayer electronic component 101 within the predetermined size range, since the volume of the electrode paste film 110 must be secured, undesirably, it is necessary to decrease the effective volume required to provide capacitance. Meanwhile, the thickness of each of the plating films 111 and 112 is about several micrometers, and therefore, if the first plating film 111 and the second plating film 112 alone can define each of the external electrodes 108 and 109, it is possible to have a larger effective volume required to ensure capacitance.
In order to form external electrodes by plating directly on the end surfaces of the laminate, it is necessary not only to precipitate plating deposits on the ends of the plurality of internal electrodes exposed at the end surfaces of the laminate but also to grow the plating deposits so as to be linked to each other. However, as the distance between the ends of the adjacent internal electrodes increases, the linking is less easily achieved even if plating growth occurs. In such a case, joining defects may occur between the internal electrodes and the plating films, or the insulation resistance may be degraded due to penetration of moisture or other contaminants.
For example, Japanese Unexamined Patent Application Publication No. 2004-40084 describes a technique that can overcome the problem described above. Japanese Unexamined Patent Application Publication No. 2004-40084 describes that the ends of dummy electrodes are exposed at locations at which the ends of internal electrodes are not exposed in regions where external electrodes are intended to be formed. Thereby, even in a region where the exposed ends of the internal electrodes are not distributed or the distribution density is low, linking of the plating deposits is facilitated. Consequently, it is possible to form external electrodes in a satisfactory state by plating. Furthermore, by using the technique described in Japanese Unexamined Patent Application Publication No. 2004-40084, it is possible to form external electrodes on side surfaces of the laminate at which the ends of internal electrodes are not exposed.
However, when the technique described in Japanese Unexamined Patent Application Publication No. 2004-40084 is used, it is necessary to form internal electrodes as dummy electrodes in addition to the original internal electrodes. Consequently, the total number of internal electrodes to be formed increases, and the internal electrode formation step becomes complicated, resulting in an increase in manufacturing cost. Furthermore, if a deviation occurs in the formation location of the dummy electrodes, or a misalignment occurs during the stacking operation for forming a laminate, dummy electrodes may not be properly exposed at a predetermined surface of the laminate. When the dummy electrodes are not sufficiently exposed, a plating film may not be uniformly formed. When the plating film is not uniformly formed, there is a possibility that joining defects may occur between the plating film and the original internal electrodes, resulting in a decrease in reliability of the multilayer electronic component.